JPH04174874A - Lap copying and conveying device - Google Patents

Abstract

PURPOSE:To prevent an uneven copying resulting from a slippage of copying papers by controlling movable the front end position of a copying paper at the double acting end when a belt is double-acted to copy the next lap image to the copying paper after the first copying is completed, corresponding to the size of the copying paper. CONSTITUTION:When the full length of the larger size of a copying paper is made lp2, and the full length of the smaller size is made lp1, the distance lAC1 subtracting the distance lR from the front end of a copying paper S(34) to the top of a driving roller 18 from the full length lp1 of the copying paper is smaller than the distance lac2. As a result, when the position of the double acting end is at a constant part Rr constantly, the inequality l'F+l'R>lAC2 is formed, and an area where a charged pattern is not formed as the amount of the difference between the left side and the right side in the inequality is formed. In order to eliminate such an area, the front end of the copying paper S when the belt 17 is double-acted to copy the next lap image to the copying paper after the first copying is completed is controlled variably. Consequently, generation of an uneven copying can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an overlapping transfer conveyance device applied to image forming apparatuses such as color copying machines, color facsimiles, and color printers.

(Prior Art) (1) An image forming apparatus which obtains a desired overlapping image by sequentially overlapping a plurality of toner images formed on a latent image carrier onto the same transfer paper is disclosed in Japanese Patent Application Laid-Open No. 58-198062 and It is disclosed in Japanese Patent Application Laid-open No. 118366/1983. In this technology, when the transfer paper held by the transfer paper conveyance means is particularly large in size, when it moves forward to transfer the image, its leading edge in the traveling direction separates from the belt and extends forward, allowing the next image to be transferred. When the belt moves back and is on standby, the rear end separates from the belt and extends rearward.

(2)Although it is not publicly known, it is also possible to hold the transfer paper on the belt by the adsorption force generated by the unequal electric field charge pattern formed in advance by the electric field charge pattern forming means on the reciprocating dielectric belt. It is used in an image forming apparatus that obtains a desired overlapping image by sequentially overlapping and transferring a plurality of toner images formed on an image carrier onto the same transfer paper, and when the belt moves forward, the leading edge of the transfer paper moves away from the belt. An overlapping transfer transfer device in which the electric field charge pattern forming means is disposed at a first position near the separating position and at a second position near the position where the trailing edge of the transfer sheet separates from the belt during backward movement. is proposed.

This unequal electric field charge pattern is formed, for example, as a charge density pattern arranged at a constant pitch on the belt by an AC voltage applied from an electrode roller at 2, which is an electric field charge pattern forming means rotated in pressure contact with the belt. be done. Due to the electric field density pattern formed in this way, an unequal electric field is formed near the surface of the belt, and this electric field causes a component of force perpendicular to the paper surface to act on the transfer paper, causing it to be attracted to the belt and shift. The belt is held together with the belt and conveyed integrally with the belt.

(Problems to be Solved by the Invention) In the technique (2) above, the end of the transfer paper comes off the belt before and after the image transfer process. This is suitable for shortening the belt and downsizing the entire image forming apparatus, but there is a risk that the paper will not be held securely against the belt, and in the case of color copying, it will cause color misalignment and This will cause a drop in quality.

On the other hand, in the technique (2) above, the attraction of the transfer paper to the belt is strengthened by the action of the unequal electric field, so the problem in the technique (2) is resolved. However, depending on the size of the transfer paper, there may be an area on the belt within the area of the transfer paper where the unequal electric field charge pattern is not formed. Then.

In this region, the image transfer conditions are different from those in the region where the unequal electric field charge pattern is formed, resulting in image unevenness.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overlapping transfer conveyance device that does not cause transfer unevenness caused by the above-mentioned reasons on all transfer sheets used in the image forming apparatus.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, in the technique proposed in (2) above, after the transfer is completed, a belt is used to transfer the next overlapping image to the transfer paper after the transfer is completed. The position of the leading edge of the transfer paper at the end of the return movement during backward movement is variably controlled in accordance with the size of the transfer paper.

In this case, when the length of the formation area of the unequal electric field charge pattern after the portion corresponding to the leading edge of the transfer paper formed on the belt during the backward movement of the belt is Lac, the electric field charge placed at the second position is It is effective to set the return end so that the length from the pattern forming means to the portion corresponding to the leading edge of the transfer paper is smaller than the Lac, regardless of the size of the transfer paper.

(Function) The belt is controlled to move backward until the formation area of the unequal electric field charge pattern formed when the belt moves reaches at least the second electric field charge pattern forming means. The lightning pattern is formed continuously on the belt.

(Example) In FIG. 2, reference numeral 1 indicates a photoreceptor belt as a latent image carrier, which is supported by a driving roller 2 at one end and a driven roller (not shown) at the other end. It is designed to be rotated.

A transfer belt 17 made of a dielectric material is disposed perpendicular to the photoreceptor belt 1 and close to and opposite the drive roller 2 . This belt 17 is connected to the drive roller 18. A driving roller 2 is supported by a driven roller 19 and is located approximately at the center in the longitudinal direction, and a transfer corona 21 is located on the back side of the belt 17 and facing the roller.

When forming a superimposed image, a latent image is carried on the photoreceptor heald 1, which is then visualized as a toner image and sent toward a transfer section, which is a belt section directly above the transfer corona 21.

Meanwhile, at the same timing, the transfer paper S fed onto the transfer belt 17 is moved to the left (forward movement) together with the belt. When the leading edge of the paper reaches the transfer section, the toner image on the photoreceptor belt 1 also reaches the transfer section, and the toner image is transferred onto the transfer paper by the action of the transfer corona 21.

In this transfer process, the transfer paper S is sent to a position where its rear end is removed from the transfer section, that is, to a position shown as point R3 in FIG. 2. The transfer paper in this state is labeled S (34)
This position is referred to as the forward end of the belt 17. At this forward end, the belt 17 immediately moves backwards to the right (backwards) together with the transfer belt 17, and reaches point R7, where the leading edge of the transfer paper S has come off the transfer section, in preparation for the next overlapping transfer. The direction of belt movement can be switched. Belt 17 at this position
This is called the reciprocating end.

Then, the process proceeds in synchronization with the arrival of the toner images for overlapping transfer formed on the photoreceptor belt 1 to the transfer section, and overlapping images are formed in the same manner as described above.

After repeating these steps a required number of times, the transfer paper S moves further to the left and is discharged from above the transfer belt 17 in order to proceed to the fixing step.

By the way, as mentioned above and as shown in FIG. 2, if the size of the transfer paper is larger than the transfer belt 17 to a certain extent, the direction of movement of the belt changes at the end of the forward stroke and at the end of the backward stroke. Sometimes, the edge of the transfer paper protrudes from the belt, making the support on the belt unstable.
A positional deviation occurs from the original position.

In order to avoid this, an electric field charge pattern forming means is provided as a means for obtaining paper adsorption force.

This electric field charge pattern forming means is an electrode roller 22.2.
2' and AC power sources 23 and 23' connected thereto. The electrode roller 22 is movably in contact with the drive roller 18 at a first position near the position where the leading edge of the transfer paper separates from the belt when the belt moves forward, that is, at a position diagonally below the left of the drive roller 18, and similarly. The electrode roller 22' is movably in contact with the driven roller 19 at a second position near the position where the trailing edge of the transfer sheet separates from the belt when the belt moves back, that is, at a position diagonally below and to the right of the driven roller 19. .

When the transfer heald 17 is moving forward, an AC voltage is applied from the AC power source 23' to the electrode roller 22' with the driven roller 19 as the opposing electrode, and when the belt is moving backward, the driving roller 18 is the electrode roller 22' that is the opposing electrode. By applying an AC voltage from an AC power source 23 to the rollers 22, a striped unequal electric field charge pattern is formed on the belt as these electrode rollers rotate.

In this way, in the combination of forward movement (normal rotation) and backward movement (reverse rotation) of the transfer belt 17, an unequal electric field charge pattern is formed over the entire belt area that contacts the transfer paper. The paper adsorption effect caused by the charge pattern prevents the transfer paper from shifting.

On the other hand, if the electrode roller 2
If there is a region where 2, 22' does not contact the belt, the charge pattern will not be formed in that region, and the image transfer conditions will be different from the region where it is formed, resulting in image unevenness.

Taking this point into consideration and referring to FIG. 2 again, when the transfer process is completed and the transfer belt 17 reaches the forward end, it corresponds to a distance of l AC from the leading edge of the transfer paper S (34). In other words, the area of the transfer belt corresponding to the area to be transferred, that is, the distance from the total length of the transfer paper IP Distance 1i (18
)" passes through the electrode roller 22 during the backward motion. Therefore, when the transfer belt 17 moves back from the forward movement end, an unequal electric field charge pattern is formed in the area of the transfer belt corresponding to the distance I Ae□.

Here, the leading edge position of the transfer paper S (33) when it reaches the backward movement end is assumed to be point R7. Then, ``distance from the leading edge of the transfer paper to the top of the driven roller! Distance fil,'+1.'
The region corresponding to is not the region to which the electrode roller 22' is passed during forward movement and a voltage is applied. That is, when the transfer belt 17 moves forward from the backward movement end, the distance is 1. An unequal field charge pattern is formed after the area of the transfer belt corresponding to +18'.

Therefore, as long as the relationship 1 r''' l Fl'< l Acz holds, an unequal electric field charge pattern is formed seamlessly on the transfer belt corresponding to the transfer paper, and in the case of Fig. 2 where the transfer paper size is large to some extent. is the above 12'+lT
Since the condition of +'<lAc is satisfied, there is no problem 1, N
.

However, as shown in FIG. 1, when the transfer paper size is small, such as the total length IP2 (1.□<1.□), the distance IAc2 corresponding to the above-mentioned IAc distance is small. Therefore, if the position of the reversing end is always the constant R7 point, l,' +1. '>1. cz, and the difference between the left and right sides of the inequality sign results in a region where no charge pattern is formed.

Therefore, in this example, after the transfer is completed, in order to transfer the next overlapping image to the transfer paper after the transfer is completed, the leading edge position of the transfer paper at the end of the backward movement when the belt is moved backward is adjusted to the size of the transfer paper. We decided to perform variable control accordingly.

In other words, when using a small-sized transfer paper, the leading edge position of the transfer paper S (33) when it reaches the backward movement end is changed to point R1, which is to the right of point R7, as shown in the figure.

This gives a distance of 1. ′ is the distance of small value 111 F ”
So 1. ” +lll'< lAc2, and a seamless charge pattern is formed.

Such control of the leading edge position of the transfer paper is performed by the configuration shown in the block diagram shown in FIG. In the same figure, information 100 for "detecting the size of one sheet of transfer paper to be used" is input to a main board 41 including a central processing unit (CPU), and based on this information, control information is applied to a servo control board 43 to transfer data. The belt drive motor 39 is controlled.

Here, "1 paper size detection" is performed as follows. A paper cassette mounting section of an image forming apparatus is provided with five sensors (photointerrupters). On the other hand, the sensor corresponding portion of one paper cassette is provided with a shielding plate designed to shield the sensor according to the size of the paper stored in the paper cassette. Therefore, paper size detection information is obtained according to the paper size detection code as shown in FIG. 4 depending on the shielding state of the sensor by the shielding plate.

In Figure 4, black circles indicate no sensor shielding.

White circles indicate that the sensor is shielded.

In this way, the belt is controlled to move backward until the formation region of the unequal electric field charge pattern formed during the forward movement reaches at least the second electric field charge pattern forming means, thereby forming the unequal electric field lightning pattern. As a result of being seamlessly formed on the belt, it is possible to obtain a good image without transfer unevenness on all transfer papers to which it is applied.

Next, a color recording apparatus will be described as an example of an image forming apparatus suitable for implementing the present invention.

In the following explanation, parts having the same functions as those in FIGS. 1 to 3 of the embodiment described above are designated by the same reference numerals. Further, the symbol Y means yellow, M means magenta, C means cyan, and Bk means black.

First, when the print switch is turned on (a in FIG. 6(1)), the photoreceptor belt 1 is rotated by the drive roller 2 clockwise by the PC drive motor 36 for driving the belt.
As shown in FIGS. 5 and 7, it rotates in the direction of the arrow at a linear velocity of vP.

At the same time, the transfer drive motor 39 for driving the transfer belt 17 first rotates in the normal direction (g, h in FIG. 6 (1)).
(see the signal and the speed diagram of j), and then start the
As shown in the figure, it rotates in the direction of the left arrow at a linear velocity of VF.

Note that each motor is controlled and driven so that these speeds rotate under the condition of VP=VF.

Now, the photoreceptor belt l is the static eliminator 3o for the photoreceptor belt.
Static electricity is removed by T! The entire surface is uniformly charged by the electric appliance 4, and the processing is performed to satisfy the following conditions.

1. The static eliminator 30 irradiates the surface of the photoreceptor belt 1 from which toner has been previously removed by the cleaner 29 with light (or applies a static eliminator corona) to remove the toner from the surface of the photoreceptor belt 1.
The surface potential of is set to approximately Ov.

2. In the case of a negative-positive process, since toner adheres to uncharged areas on the photoreceptor surface, the entire surface of the photoreceptor belt 1 must be uniformly charged by a charger.

3. The charger performs uniform charging by corona discharge, but
A slight amount of ozone is generated by discharge. Although this ozone decomposes in a short time when the discharge is stopped, it may have an adverse effect on the surface of the photoreceptor belt 1 and impair the sharpness of the image. Therefore, the influence of ozone is eliminated by blowing air from behind the charger using a fan or the like (not shown) or by sucking air.

By the way, a one-rotation sensor is installed on the shaft of the drive roller 2, and a detection pulse is output every time the drive roller 2 makes one rotation (d in FIG. 6(1)).

In the example of FIG. 6 (1), at the timing of the third pulse of this one-rotation detection sensor, the semiconductor laser (hereinafter abbreviated as LD) of the optical writing unit 5 is used. type of laser or LED array,
The optical writing unit (which may be another optical writing unit such as an LCD array) is controlled and driven, and first, optical writing based on seven image data is started to form an electrostatic latent image (d in the same figure).

This image data and other image data that follows are read by a color image reading device (not shown) in blue, green, red,
The three color separated lights are read respectively, and image calculation processing is performed based on the intensity level of each color light to determine Y, M
, , C, and Bk.

Apart from this, other color image processing systems (e.g.
The image data may be input from a color facsimile, a personal computer, etc., and the connection interface for that purpose may be individually supported.

By the way, the developing device for visualizing the electrostatic latent image 7.9.11.
13 is normally located at a position where the developing roller 6.8.10.12 does not come into contact with the surface of the photoreceptor belt 1. Then, only from just before the latent image surface of the corresponding color reaches the position of the developing roller of each color to just after passing through, the developing device of the corresponding color, in the example of FIG. 5, the developing roller 6 is pressed to the left. The photoreceptor is then set at a position where it is in a predetermined contact state with the surface of the photoreceptor.

At the same time, in order to provide only that developing device with a developing function, driving of the developing roller and the parts contributing to development is started (m=p in FIG. 6(2)).

Now, since seven latent images have already been formed as described above, the developing roller 6 of the Y developing device is brought into contact with the photoreceptor surface at the appropriate timing and is driven (as shown in FIG. 6 (2)). m) and visualize 7 images.

The next step is the transfer process, and the roller for switching between contact and separation is moved so that the transfer belt 17 contacts and separates from the surface of the photoreceptor belt 1 at the transfer portion (point T where the drive roller 2 faces the transfer belt 17). 20 vertical positions are switched.

When the transfer operation starts in this way, the transfer belt 17 is driven in the direction of the left arrow as described above, and then the roller 20
is pressed to the upper position to bring the transfer heald 17 into contact with the photoreceptor belt 1 (FIG. 6(2)).

Then, at a predetermined timing, the transfer paper 14 is transferred to the transfer roller 1.
The paper is fed at step 5, and then transported by registration rollers 16 at a timing that matches the position of the image formed on the photoreceptor belt 1.

The conveyed transfer paper S is inserted along the transfer belt 17. It should be noted that static electricity removal from the transfer belt is performed uniformly over the entire surface. Further, at this time, a cleaning process is also being performed by the transfer belt cleaner 25.

Now, when the leading edge of the 7 visualized images reaches 18 points at a predetermined distance from the transfer position point T, the transfer drive motor forward rotation start signal S□ (h in Fig. 6 (1)) is applied to the transfer drive motor. The information is input to the servo control board 43. However, at the time of the transfer drive motor normal rotation start signal S1, the transfer drive motor is already rotating in the normal direction, and the normal rotation operation continues for M times (j in FIG. 6(1)).

The timing of the transfer active motor forward rotation start signal S is substantially when the leading edge of the transfer paper reaches the RT point, that is, the position 1 in the front direction of the transfer position T, and also when the photoreceptor heald 1 7 Image tip is at position T 1□ in front of point T
This is the point when point s is reached.

In the example of FIG. 6 (1), this is the time when the drive roller 2 has rotated four times and the PCC auxiliary motor 36 has rotated by an amount equivalent to the encoder pulse number PO (see FIG. 6). (1) d, 'e, f, h)
- During this time, the photoreceptor belt 1 is at point E (image writing position)
It has moved the distance from to point Ts.

Time t from the time of transfer drive motor normal rotation start signal S1
After □ has elapsed, the leading edge of the 7 images and the leading edge of the transfer paper both move a distance of 1 □ and reach the transfer position T, and thereafter the Y image is transferred by the transfer corona 21.

PCI at this time □! 7 motion motor encoder 3
7 is the number of pulses P and the number of pulses of the transfer drive motor encoder 40 is PTl (e, k in FIG. 6(1)). Here, as the resolution of both encoders, if the belt movement dimension per pal person is the same, then P =
If PT□ and the ratio of the two is α, Pl and PT will have values corresponding to the coefficient α.

In this example, the following description will be made on the condition that P□=PT work.

Now, as the seventh image transfer process progresses, the leading edge of the transfer paper separates from the transfer belt 17, passes over the solid line position of the path switching member 26, and advances toward the paper leading edge guide plate 27.

Then, seven more image transfer steps proceed, and the trailing edge of the transfer paper becomes
From the time when the transfer paper passes point T by a distance of 1□, that is, from the time when the transfer drive motor forward rotation start signal S is received, the transfer paper moves to 1□+I
Time t□ to move a distance of P (transfer paper size) + 12
+tz) (at this time, the transfer paper is 1 indicated by S (34)
The transfer drive motor is rotated in the reverse direction by the transfer drive motor reverse signal (1.j in Figure 6 (1)).
).

Prior to this reverse rotation, the roller 20 is lowered to the lower position to separate the transfer belt 17 from the belt surface.

Due to reverse rotation, the transfer belt and transfer paper move in the direction of the right arrow.
Make a quick return at a speed of (>VF).

During reverse rotation, the transfer paper and the transfer belt 17 carrying the transfer paper are
An AC power source 23 is connected between the drive roller 18 as a counter electrode and the electrode roller 22 for creating a charge pattern during reverse rotation.
A voltage is applied and a charge pattern is created (Figure 6 (
2) W).

As a result, a suction force is obtained at the leading end of the transfer paper S, which is located between the transfer belt 17 and the transfer belt 17 .

At this time, in a short time t, 1. The position is controlled to the right by a distance equal to the distance moved to the left by +12, and the position is returned.

During this return, the trailing edge of the transfer paper is separated from the transfer belt 17 and advances toward the paper trailing edge guide plate 28. Then, return the specified distance accurately and the transfer paper will be 5 (33)
It stops at the dashed-dotted line state position (the leading edge position of the paper is at point R) and waits for transfer of the second color M image (for a time tj).

On the other hand, on the photoreceptor belt 1, the second color M image is already being formed even while the first color Y image is being transferred. That is, the formation of an electrostatic latent image by optical writing by controlling and driving the LD based on the M image data starts at the point when the drive roller 2 makes an integer number of rotations (4 in FIG. 6 (1)) from the start of Y image writing.
It starts at the point when it rotates.

Then, in the developing device, the developing roller 6 of the Y developing device 7 contacts and is driven only in the 7th image area, and before the second color M image area arrives, the developing roller 6 is separated from the photoreceptor belt 1 and the driving is stopped. will be stopped.

Instead, the developing roller 8 comes into contact with the photoreceptor belt 1 and is driven (n in FIG. 6(2)) after the image area has passed but before the leading edge of the M image area reaches the M image area. Only the image area is visualized into an M image.

Next, when the leading edge of the 1M image reaches the Ts point, that is, as in the case of the first color Y image, from the M image data writing start timing, the drive roller 2 rotates 4 times and the PC drive motor encoder 37 pulses. When the transfer drive motor has rotated by an amount corresponding to Pa, a transfer drive motor normal rotation start signal S2 is inputted to the transfer servo control circuit 43.

At the same time or with a slight delay, the contact/separation switching roller 2o starts a pressing operation in the upward position direction and is brought into contact with the transfer paper until at least the leading edge of the transfer paper reaches the T point.

Furthermore, at the timing of the start of forward rotation, an AC voltage 23' is applied between the electrode rollers 22' for creating a charge pattern during reverse rotation using the photoreceptor belt 19 as a counter electrode to form a charge pattern (FIG. 6 (2)). X). As a result, a suction force is obtained at the rear end portion of the hexagonal belt 14 that is spaced apart from the photoreceptor belt 17. Further, at the start of printing, an AC voltage 23'' is applied in the same manner as described above to eliminate static electricity from the photoreceptor belt 17 (X in FIG. 6(2)).

Now, at time t from the timing of the transfer drive motor normal rotation start signal S2, the photoreceptor belt 1 has a pulse number of the encoder 37 of P, and a PC belt surface movement distance of 1□, as in the case of the previous 7 images. ing.

Therefore, during this time t1, the transfer paper S is also started up from the state of speed O to VF= (VP), and during this time, the transfer drive motor for the first color receives the forward rotation start signal S at the time □. In this case as well, position control is also performed so that the two coincide, as in the case of distance scanning 1□.

As a result, here too, the leading edge of the transfer paper is moved at a distance of 1 in time t.
This means that the seven images of the first color and the M image of the second color are aligned on the transfer paper.

Thereafter, repeat the same steps as above. That is, the process proceeds to M image transfer, transfer paper quick return, Bk image data writing, Bk development, and Bk image transfer.

Next, the process after transferring the Bk image will be explained.

In the Bk image transfer process, the path switching member 26
Point g! After switching to the line position, the transfer paper during the transfer process advances toward the fixing device 31, and even after the transfer of the trailing edge of the transfer paper is completed, the transfer drive motor 39 continues to rotate normally and transports the transfer paper to the left. Then, the fixed color print is carried out to the tray 32 (J+u* in Fig. 6 (1) and (2)).
v).

When performing a repeat operation as in the case of Fig. 6, after writing the Bk image data on the first sheet, proceed to write the Y image data on the second sheet as shown in the same figure. The operation control is also the same as from the beginning of the first sheet.

Note that the photoreceptor belt 1 has residual toner removed by a cleaner 29 , residual charge is further removed by a static eliminator 30 , and the photoreceptor belt 1 moves toward the charger 4 .

Finally, after the last color print is delivered to the tray 32 and the photoreceptor belt 1 and transfer belt 17 are cleaned, the operation is stopped and the initial state is restored.

In the above description, the order of image formation is Y, M, and C.

Although Bk has been used, the present invention is not limited to this.

In addition, although the electrostatic latent image formation for each color has been explained using a method in which digitally processed color image data is optically written using an LD, etc., an analog optical image of a normal electrophotographic copying machine is placed at the E point position at a predetermined position. Similar color recording can also be performed by controlling the timing and position of the image to form an image.

Up to this point, we have explained four-color overlapping recording of Y, M, C, and Bk, but in the case of these two-color or three-color overlapping recording, image formation and transfer of the necessary colors must be performed consecutively. The operation of each part is controlled so that this process is completed in two or three times.

In the case of single-color recording, the developing device of that color is brought into contact and driven until a predetermined number of sheets are completed, and the transfer belt 17 remains in contact with the photoreceptor belt 1, and the path switching member 26 is held at a position where the transfer paper is guided toward the fixing device 31 and performs a recording operation.

Therefore, in repeat recording, the print production speed is 4/3 times faster when recording three colors, twice as fast when recording two colors, and four times faster when recording single colors due to the sedimentation during four colors recording.

The developing color is not limited to the above four colors, and it is also possible to use a combination of blue, green, red, and other desired colors as needed.

The above is the explanation based on the embodiment shown in FIG.

Further, each timing of the transfer belt 17 and the transfer paper S will be explained in detail.

At the position of the transfer paper S (34) where the Y image has been transferred, a portion of the transfer paper S on the transfer belt 17 is attracted to the transfer belt 17 by the transfer current of the transfer corona 21. However, the portion of the transfer paper S that is away from the transfer belt 17 has no suction force.

Here, the drive roller 18 rotates in the opposite direction, and the transfer belt moves in the direction of the arrow VR force. At that timing, the AC voltage from the AC power supply 23 is applied to the drive roller 1 via the electrode roller 22.
8 is applied as a counter electrode.

As a result, a slit-shaped charge pattern is formed on the transfer belt 17, and an unequal electric field is generated.

This unequal electric field is caused by the transfer paper S which has lost its adsorption force.
It functions to re-adsorb the portion of the transfer belt 17 that has separated from the transfer belt 17.

In this re-adsorption, as shown in FIG.
A charge pattern is formed by using the transfer paper as a counter electrode, but unless the transfer belt 17 is moved while the transfer paper is in contact with the circumferential portion of the drive roller 18, the attraction force due to the unequal electric field will not be generated.

Next, when transferring the M image, that is, the transfer belt moves in the VF force direction, the transfer paper 5 (33) is at the position shown in the figure, the trailing edge of the transfer paper leaves the driven roller 19, and the next transfer starts. At this time, an AC voltage from the AC type g23' is applied via the electrode roller 22' to the driven roller 19 as a counter electrode. As a result, the photoreceptor belt 14 is re-adsorbed in the same manner as on the drive side.

In this way, in single-layer transfer, when a slit-shaped charge pattern is formed on the transfer belt 17 when the transfer belt returns, and an uneven electric field is generated, the leading edge of the transfer paper S (34) that has separated from the transfer belt 17 Equalize the potential of the part that meets the transfer belt again at the time of return and the rear end part of the transfer paper S that remains on the transfer belt without peeling off, and
The suction force of the transfer belt 17 is maintained. The rear end is also 2
The same effect can be obtained by maintaining the adsorption force after the ogle and when returning.

Generally, in one-overlap transfer, it is necessary to increase the transfer current during the second transfer (second color) by the transfer current during the first transfer (first color) to apply an electric field equivalent to that during the first transfer. This is because the potentials of the transfer paper and the transfer belt increase to some extent during the first transfer.

In this manner, in the transfer of four colors, a considerably large current (actually about 1 mA) must be applied to the fourth color. However, in this example, the electrode rollers 22, 22' and the AC power source 23
．． 23', the second, third, and fourth colors can be transferred with the same transfer current as the second color.

When carrying out the present invention, in FIG. 6(1), when a small-sized transfer paper is used, the time point at which the transfer drive motor normal rotation start signal h is generated is shifted to the left.

(Effects of the Invention) According to the present invention, it is possible to provide an overlapping transfer conveying device that does not cause transfer unevenness caused by transfer paper on all transfer papers used in an image forming apparatus. 6

[Brief explanation of drawings]

1 and 2 are diagrams illustrating the main parts of the overlapping transfer conveyance device according to the present invention, FIG. 3 is a block diagram suitable for implementing the present invention, and FIG. 4 is an explanatory diagram of the paper size detection code, FIG. 5 is an overall configuration diagram of a color recording device as an example of an image forming device to which the overlapping transfer conveyance device according to the present invention is applied, FIG. 6 is a timing chart explaining the basic operation of the same device, and FIG.
The figure is a drive control block diagram. 17... Transfer belt, 22.22'... Electrode roller, S, S (33), S (34)... Transfer paper. --- Osamu Ichiyo
Toru Kabayama; (1 idiot)

Claims (1)

[Claims] 1. While holding the transfer paper on the belt by the adsorption force generated by the unequal electric field charge pattern formed in advance by the electric field charge pattern forming means on the reciprocating dielectric belt, It is used in an image forming apparatus that obtains a desired overlapping image by sequentially overlapping and transferring a plurality of toner images formed on an image carrier onto the same transfer paper, and when the belt moves forward, the leading edge of the transfer paper moves away from the belt. An overlapping transfer transfer device in which the electric field charge pattern forming means is disposed at a first position near the separating position and at a second position near the position where the trailing edge of the transfer sheet separates from the belt during backward movement. After the transfer is completed, in order to transfer the next overlapping image to the transfer paper after the transfer is completed, the leading edge position of the transfer paper at the end of the backward movement when the belt is moved back is adjusted according to the size of the transfer paper. An overlapping transfer conveyance device characterized by variable control. 2. In claim 1, when the length of the formation region of the unequal electric field charge pattern after the portion corresponding to the leading edge of the transfer paper formed on the belt when the belt moves is Lac, The overlapping transfer conveyance device is characterized in that the return end is determined so that the length from the electric field charge pattern forming means to the portion corresponding to the leading edge of the transfer paper is smaller than the Lac, regardless of the size of the transfer paper. .